I spent a few hours poring over the service manual and some related datasheets to produce the following image of the Casio SK-1 PCB. In the image I have labeled all of the unique pins from the RAM/ROM chips, as well as the unique pins of the JA and JB busses (primarily the keyboard matrix). Additionally, I labeled all of the MCU pins.

The image is 4800x1800. Please ignore the nasty soldering on the middle RAM chip -- leftovers from removing the previous bends. I'll clean all that up.

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